In various types of electric equipment products and electronic equipment products, conducted noise generated from a power line, communication line, or the like connected to electric equipment or electronic equipment needs to be restricted by EMC (Electromagnetic Compatibility) regulations or the like. Accordingly, a noise filter is connected between the commercial power line and various types of electronic equipment. However, such a noise filter cannot provide desired noise attenuation characteristics, so a technique for effectively suppressing noise needs to be developed.
For example, the technique disclosed in PTL 1 is known as a technique for improving the noise attenuation characteristics of such a noise filter. The technique disclosed in PTL 1 proposes to insert an electric conductor connected to a structure (such as the chassis or cabinet of a vehicle) kept at the ground potential between two common mode choke coils in a noise filter including common mode choke coils, capacitors, and the like.
The conventional art described above improves the noise attenuation characteristics that degrade due to the stray static capacitance caused by the windings of the common mode choke coils by breaking the coupling between the common mode choke coils due to the stray static capacitance present between the two common mode choke coils using the electric conductor inserted between the two common mode chokes. In addition, the conventional art improves the noise attenuation characteristics using the stray static capacitance generated between the common mode choke coils and the electric conductor as a line bypass capacitor that bypasses noise to the ground potential part.